The use of solenoid operated two-way valves in internal combustion engines has been ongoing for many years. These types of valves can be used in a variety of different applications to control the flow of fluid through a fluid circuit. For example, U.S. Pat. No. 4,905,960 to Barnhart et al. discloses a solenoid operated two-way valve for controlling the flow of fuel into a timing chamber of an electronically controlled unit injector to permit control over both the quantity and timing of fuel injected into the combustion chamber of an internal combustion engine. In addition, two-way valves are advantageous for controlling the spill or backflow of fluid from a fuel injector or other engine component.
Effective operation of two-way control valves during engine operation is critical to overall engine performance. If a valve is unable to open or close under various engine conditions, or is inadvertently opened or closed at an inappropriate time during operation, then the benefit of a control valve becomes moot. To ensure effective operation, a control valve must be designed and manufactured to withstand a variety of conditions which exist in an internal combustion engine, such as high pressures. Specifically, fluid pressures acting on a valve element of a two-way valve may provide enough force to close or open the control valve prematurely which could have undesired consequences. In particular, certain control valves that are not pressure balanced, such as disclosed in U.S. Pat. No. 4,905,960, are susceptible to uncontrolled valve closing or "blow shut" when fluid pressure forces overcome the spring force which maintains the valve in an open position. This may occur during normal supply flow and reverse supply flow conditions. Under normal engine operations, "blow shut" should not occur. One proposed solution for preventing "blow shut" is to increase spring preload. However, an increased biasing force requires a solenoid capable of generating greater pulling loads to overcome the biasing force thereby undesirably resulting in a larger, more expensive solenoid assembly. Another possible solution is to use a pressure balanced valve structure. However, a pressure balanced valve design would undesirably introduce an additional leakage path. At very high flow rates, the above solutions would not be practical and would significantly increase manufacturing costs.
Ideally, a solution which utilizes existing valve architecture to address the problems of conventional valve designs would be desired. U.S. Pat. No. 4,582,294 to Fargo discloses a three way solenoid valve wherein an inlet is defined by an orifice which causes fluid flow to act upon the valve in the opening direction of the valve before the fluid flow direction is again reversed. The solenoid valve of Fargo is pressure balanced in an open position and does not appear to be influenced by fluid pressure forces acting to close the valve. Fargo does not recognize the "blow shut" problem and therefore does not provide a solution for counteracting fluid pressure forces acting to close the valve.
In order to effectively and practically prevent the problem of "blow shut" during normal engine operating conditions as discussed above, a flow control valve having a simple design to counteract adverse fluid pressure forces acting to close the valve is needed. Moreover, the magnitude of counteracting forces should be adjustable in order for a user to custom design the flow control valve for specific applications. Finally, a flow control valve having an increased flow capacity while preventing the occurrence of "blow shut" during normal operating conditions is also desired to improve upon the current flow control valve designs.